1) If metaphysical realism is true, then global skepticism is possible
2) If global skepticism is possible, then we can be brains in a vat
3) But we cannot be brains in a vat
4) Thus, metaphysical realism is false
1) Assume we are brains in a vat
2) If we are brains in a vat, then "brain" does not refer to brain, and "vat" does not refer to vat (via CC)
3) If “brain in a vat” does not refer to brains in a vat, then “we are brains in a vat” is false
4) Thus, if we are brains in a vat, then the sentence “We are brains in a vat” is false
I don't believe there is a way out of the skeptical hypothesis. — shmik
For instance, I could still say 'it's possible that when I was 12 a mad scientist placed my brain into a vat and I have been living in a vat ever since'. This formulation would allow me to refer to brains in vats. — shmik
You can't know the answer to questions like this with certainty. You can't prove empirical claims.How can I know that I am really here typing this message and not just a brain in a vat as Putnam challenges us to prove? — Jamesk
By denying the realist's claim that "truth is not reducible to epistemic notions but concerns the nature of a mind-independent reality"1, which was Putnam's goal. — Michael
instead the words "brain" and "vat" as spoken by a BIV person refer to simulated brains and simulated vats. — Michael
Once we take the view that we are somehow experiencing the mental, there is no way for us to use thought (further mental) to think our way to the 'real' world. — shmik
Re Putnam, by the way, I don't at all agree with his argument, because I don't at all agree with his views of how meaning works.I'm going to be pedantic and point out that your question misrepresents Putnam. — Michael
I wander about this - it's been a while since I've read Putnam so I might try to read an SEP article on it later. Why would realism entail that I always have access to / be able to refer to / mind independent reality?However, given the causal constraint on reference, you could never refer to the real brain in a vat that you are (and always have been), and so realism entails a necessary falsehood, refuting itself. — Michael
But the real world is conceptually articulated through and through; so why would we need to "make our way there"? On the contrary, it cannot be escaped... — John
Obviously naive realism is true.
Putnam decisively refutes the skeptic idea that we might just be brains in a vat. For example, in Reason, truth, and history (1981).
Apparently it's available online at https://www.archive.org/stream/HilaryPutnam/PutnamHilary-ReasonTruthAndHistory_djvu.txt — jkop
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